Unfortunately there is a little more to it than just swapping out the driver ...
To date the best 4.2v driver I know off is the one in my MTE , just try getting one though ! [ There expensive if you have to buy the MTE to get one ]
Yes Shinning beam driver is a good one ... And 3 modes , so no junk ..
http://www.kaidomain.com/ProductDetails.aspx?ProductID=1845 Best cheap driver I know off , used it on everything from Cree P4 to SSC P7 / MC-E .. Ive used it with SSC P4 - Diamond Dragons - Luxeon K2 TFFC - Cree XR-E R2 to XP-G R5 .. Should keep a few in stock if you do mods ...
Ok , the emitter itself will matter , if you get one thats got nice low voltage forward [ LED's operating voltage ] , the lower the better with 4.2v drivers , then you will see good performance ...
If on the other hand the vF is on the higher side , then you will see lower performance .. Then there is also the battery , a good battery will outperform a bad one .
In my MTE , a bad battery may do 2.2A [ SSC P7 ] , whilst a good one may see 3.5A or better , thats just a huge variation , one which you must take into consideration .
If you buy cheap cells , you cant expect stellar performance ... In the end its a combination of all the variables , and to some extent pot luck . Though when it comes to the P60 performance pills , SSC P7 / MC-E , I do get the feeling , that possibly the MC-E might be the better option , especially when swapping out drivers ... From the reports coming in , the SSC P7 seems to suck , and one might be better off with a XP-G R5 , maybe .