Seem to remember someone on BC had the Burton upgrade and were not particularly impressed, certainly didn't get to 160 bhp.
Shawspeed claim to get 150-160bhp with throttle bodies etc, and beyond 200bhp with ported cylinder head, oversize valves etc etc but at high cost. here
Pro-tune also quote high outputs here
Personally I would go for cc upgrade if you want to keep you current car, this would make it easier to sell through cc if you want to trade it in.
The other option is to simply trade up to a Duratec as this permits further upgrades if needed, and may be less expensive in the long run. 2.8K is a considerable sum for an extra 25bhp.