Thanks you for a very detailed explanation @Grant.

There might be few differences in the number of rows from fast - slow instance. That is because Fast instance is currently LIVE production instance and it might just have 1 days transactions so the difference would be minimal and also when i tested it was like-to-like and the execution plan was the same for fast instance.

I updated the stats using the command :

EXEC sp_MSForEachTable 'UPDATE STATISTICS ? WITH FULLSCAN;'

However i will rebuild / reorganize indexes and test it again and will update here.

I would also guess this could be something due to Standard v Enterprise edition.