Firstly, I could definitely go with SilverShelby and stay with Silver Cans. That way, I can put Grandpa back to work! TCS-handout system works fine...
Nextly, what BL motors are you guys using? The TCS-legal Novak and Reedy have adjustable endbell timing. Guarantee, crank that timing up to 60* and you will be MUCH faster than SCans. And that's with TCS-legal 0* timing speedos, which cost less than $100. Also guaranteed to fry some motors...but you know the old saw about how fast do you want to go?
If cost is the biggest concern, Silver Cans hands down. They are only $15 and we all already have the speedos. My biggest concern is keeping ONE BIG COMPETITIVE HEALTHY CLASS. Out here, if you don't count my goofy buddy SirSpeedy , we haven't had the same guy win two races in a row in years! That's competitive.