Howe long will it last

Need some advice I've just installed a mallossi multivar 2000 and when you buy the variator you get 21 24 28 gram rollers with it all for £197.00 bargain first impressions are bloody he'll why didn't I do this earlier .very strong acceleration especially when wot I'm running 21grams at the moment .70mph equals 5600 revs with standard variator and 26g rollers 70 was5500 so no real change at 70 then .my concern is that will the 21g rollers put any more streess on the engine than the 26g ones as you know swing has a lot of miles on so don't want to break it. Cheers for any advice on my concerns