Seeing as no one else has offered an opinion...
I don't think the couples named John and Eleanor in Marylebone and St Saviour are the same couple. Looking at the baptisms in both places, if it was the same couple, they would have to be moving back and forth which seems unlikely. It doesn't help that there are several couples named John and Eleanor in Middlesex/London/Surrey around this time though.
It doesn't rule out Elizabeth being your Elizabeth though, proving it is the tricky bit.
Just in case anyone else feels like taking a look...
Baptisms - St Marylebone:
11 Apr 1819 Elizabeth; trade; born 12 Mar 1819
04 Feb 1821 Jane; mech?; born 22 Dec 1821
22 Sep 1822 Charles; trade; born 17 Aug 1822
21 Sep 1825 Emily; Harcourt St; carpenter; born 15 Sep 1824
I've included Jane, bap. 1821, even though the father's occupation is 'mech' (merchant?) just for completeness of records with parents named John and Eleanor.
Baptisms - St Saviour:
08 Jan 1815 Eleanor; Guildford St; carpenter; born 13 Dec 1814
17 Nov 1816 John Arthur; Guildford St; carpenter; born 30 Sep 1816
02 Jun 1822 Mary; Red Cross St; carpenter; born 08 Jul 1818
02 Jun 1822 Joseph; Red Cross St; carpenter; born 20 Mar 1821
05 Oct 1823 Sarah Ann; Red Cross St; carpenter; born 11 Mar 1823
03 Oct 1830 Ann Adelaide; [source=FS]
25 Nov 1832 Maria; Guildford St; blind maker; born 21 Sep 1831
11 Nov 1835 Thomas; Guildford St; blind maker; born 26 Apr 1833
11 Nov 1835 William; Guildford St; blind maker; born 04 Jul 1835
Family in St Saviour:
1841 census - Saint Saviour, Southwark
Eleanor White with children Ann, Maria and William, living with married son John Arthur and his wife Harriet (Maycock?).
Ref HO107; Piece 1088; Book 3; Folio 40; Page 12;
https://www.familysearch.org/ark:/61903/1:1:MQKQ-F4P1851 census - Saint Saviour, Southwark
Eleanor White with son William.
Ref HO107; Piece 1558; Folio 510; Page 65;
https://familysearch.org/ark:/61903/1:1:SGKQ-83ZPossible GRO BMD references:
1839 Q4 Marriage - John Arthur White & Harriett Martha Maycock; Newington; 04; 345
1844 Q1 Birth - Harriet Eleanor Ann White (mmn: Maycock); Saint Saviour; 04; 500
1846 Q1 Birth - Jane White (mmn: Maycock); Saint Saviour; 04; 569
1847 Q4 Birth - John George White (mmn: Maycock); Saint Saviour; 04; 518
I had a look for Emily White, baptised Marylebone 1825, born Sep 1824, and found a possible marriage:
GRO reference:
1850 Q4 Marriage - James Balls & Emily White; Shoreditch; 2; 465
married: 01 Nov 1850; St Leonards, Shoreditch; banns
groom: James Balls (x); fa; bach; carpenter; High Street
bride: Emily White; fa; spin; -; High Street
grooms father: James Balls; sergeant
brides father: John White; carpenter
witnesses: Charles Steel?, Charlotte Steel?
I couldn't find this couple in subsequent censuses in Middlesex though. However, I could find a couple in Essex that very closely matched this couple, and for whom I couldn't find a marriage, so it's possible this marriage is a red herring.
References for the couple in Essex:
1841 census - Hutton, Essex
Emily (recorded as Emma) with mother Sarah, pre-marriage.
Ref HO107; Piece 322; Book 17; Folio 4; Page 3;
https://www.familysearch.org/ark:/61903/1:1:MQ28-SMQ1841 census - Purleigh, Essex
James with parents James and Margaret, pre-marriage.
Ref HO107; Piece 327; Book 22; Folio 30; Page 20;
https://www.familysearch.org/ark:/61903/1:1:MQ2N-Z8W1851 census - Hutton, Essex
James and Emily with Emily's mother Sarah.
Ref HO107; Piece 1774; Folio 244; Page 12;
https://www.familysearch.org/ark:/61903/1:1:SGVF-HT41861 census - Ingrave, Essex
Ref RG09; Piece 1075; Folio 176; Page 3;
https://www.familysearch.org/ark:/61903/1:1:M749-33V1871 census - Ingrave, Essex
Ref RG10; Piece 1657; Folio 40; Page 10;
https://www.familysearch.org/ark:/61903/1:1:VFFG-5R31881 census - Ingrave, Essex
Ref RG11; Piece 1757; Folio 67; Page 24;
https://www.familysearch.org/ark:/61903/1:1:VFFG-5R31891 census - Ingrave, Essex
Ref RG12; Piece 1381; Folio 137; Page 18;
https://www.familysearch.org/ark:/61903/1:1:Q27D-4GFZ1901 census - Ingrave, Essex
James, widowed, with sister Ann.
Ref RG13; Piece 1665; Folio 55; Page 7;
https://www.familysearch.org/ark:/61903/1:1:X9ND-X57Possible GRO BMD references:
1851 Q3 Birth - John Balls (mmn: White); Billericay; 012; 10
1853 Q3 Birth - James Balls (mmn: White); Billericay; 04a; 103
1857 Q4 Birth - Sarah Balls (mmn: White); Billericay; 04a; 116
1860 Q3 Birth - Luke Balls (mmn: White); Billericay; 04a; 112
1862 Q3 Birth - Mary Balls (mmn: White); Billericay; 04a; 125
1864 Q3 Birth - George Balls (mmn: White); Billericay; 04a; 138
1901 Q1 Death - Emily Balls; age 73 (born c1828); Billericay; 04a; 298
1908 Q1 Death - James Balls; age 78 (born c1830); Billericay; 04a; 347
Baptism - All Saints, Hutton - SEAX D/P 143/1/4:
10 Aug 1828 Emily White; John & Sarah; carpenter; Hutton; page 25, no 195