My X-flow wears a SPR rocker cover as well.
When I was lookign at purchasing my 7 (gulp - 7 years ago 😳) I spoke to Roger king at length about the engine. He assured me at the time it the engine was "very solid, and built to a nice spec"
I since added a drysump, and a couple of other bits
I have to say that whilst I have owned the car, the engine has been pretty much faultless. (About 4 years ago, I had the bores "glazebusted" and new rings fitted as it started to smoke a little on the overrun - been fine since)
Although I never thrash it from cold, I am not nescessarily the kindest person to it, and tend to drive it to within an inch of its life.
The car did the USA2005 trip with not so much as a hiccup, and many of you will have seen it on trackdays as well.
On 2 independant rolling roads, (after settign up & tweaking the carbs) it has produced around 185bhp, and it seems to keep up with 200bhp K-series caterhams pretty well (until I have to stop for fuel 😳) At full chat on track I reckon its comfortably into single figure mpg!