In other "news" i bought a used (but very good condition) N900 a couple of days ago, and have now tested the stock (1320mAh) battery to confirm that it has not been used much.
Capacity of 1 year (lightly used) BL-5J original battery is now 1220mAh, so in 1 year (and lightly used) it has lost 100mAh (9%), now if it had been used like we use our N900 it would be much more, like at least 200-400mAh.

Conclusion, if you have a 1 year old battery and get a SCUD you will REALLY get a boost in battery life, for arguments sake lets say your battery has lost 200mAh then you will get 35% more battery out of the SCUD.