Aftermarket rollers dont increase performance. But the Malossi rollers are a favourite of many because they work well and last reasonably long. Dont get cheap rollers, they wear out stupidly fast.
4.1? mm i put 4.5's in mine before and it just revved the tits off it, i put my 5.5's back in and it runs fine, i've tried 6's and they're a bit heavy, 5.5s are niice
just cus we have the same bike doesn't mean we should have the same weight of rollers or even similar, different set ups work differently depending on what you got, 4.1's are working really well at the moment. and roxs come with 5.5 as standard? what have you got on your bike?