A well set up .21 will blow away any .28 in top speed and it will also run longer as the fuel econamy is better, .21 engines run much higher RPM's which + higher speeds, I guess thats why most real race engines are .21's.
We have had people come to our track with the Hoboa hyper 7's and to be honest not one of them has survived the day, the plastic is thick,yes, but it is also brittle and breaks to easy. A friend has got a Ansman VIRUS and it rips, tough like the KYOSHO buggies just a tad heavy but its burly.
Quick question for FOXY, dont KYOSHO make there own engines??? I always thought they did. If not, who is it that makes them??? I like to race every now and then and beleave it or not actually like the GX.21, although I have modded it to kingdom come, it'll blow a E-revo with brushless power away no problems be it top speed or pure acceleration. Any thoughts??? I also drive with an RB C6 buggy engine but it will not out run my GX.21 and drinks to much fuel. Average run time from my GX is around 16 minutes and on the same track with the RB C6 around the 12 minute mark.