I put reverse on a viper once and never noticed any difference in top speed, very minimal if there was a difference. Don't really know if it effected e/t but didn't notice so it must have been minimal also if any. Well worth having though. Vipers are not geared for top end like the srx, your top gear on the srx has 1 more tooth than the viper one, as long as u keep that srx gear u shouldn't notice a difference