Why get 555s when 740s are the same price? Put another way, you are getting a 300cc increase for the same price as a 115cc. 115cc isn't that big an increase over the standard 440s, unlike the S14 which has 185cc difference. Top feeds are capable of handling higher duty rates (I'm told), however, it doesn't sit comfortably with me running higher than 80%. 80% duty on 440s is 282bhp. 80% on 555s is 355bhp. 80% on 740s is 473bhp. OK, 555s may be fine, by like I said, same price as 740s. You have to get a custom map either way...
And for those thinking of an off-the-shelf chip... Topper's setup is almost identical to mine, so Jez applied my map as an initial base for the road mapping. Topper still got det initially. Off-the-shelf chips are great, but have to err on the side of caution for all the cars they might be fitted to. This means your engine isn't optimally tuned.