Aol, there's a small trick for those of us who use an ELM v1.3 compatible OBD reader (such as the current OBDkey) by which you could improve the scan rate a fair bit.
When you request a pid, instead of sending e.g. "05" you can send "05 1". I've tried this in my car and when I send "05" I get response times from 120 to 160ms (so about 6-8 fps). When I send "05 1" response times drop to 80 to 110 (ie 9 to 12 fps).
Given how little change this should require in the code, I really hope you could implement this.
The technical reason behind it for those interested:
When the OBD interface requests data from the car it doesn't know how many message it will receive as answer from the difference systems in the car or when it will happen. Hence it has a timer included which it waits for to run out. Only when during that time no new message comes in, it returns them to the software (ie RaceChrono). New ELM versions allow to specifiy how many messages to expect so it can skip one wait cycle.
So when you send 05:
<elm sends CAN request>...<wait>...<CAN response 1>...<wait>...<elm sends CAN response to RC>
And when you send 05 1:
<elm sends CAN request>...<wait>...<CAN response 1><elm sends CAN response to RC>