Discovered this tonight. Pretty fun and decently long (as far as Newmarket runs go anyway). You just bomb Southward down Joe Persechini and then make a right onto Shoniker, and then finish up with a left onto Oaktree Crescent (the second left). I find that it's mostly enjoyable because it starts pretty steep and then really mellows out, but you just carry most of your speed along the whole thing. Anyway, there's one 4-way stop sign at the beginning that you burn through pretty fast, so it can be a bit sketchy if you're not hitting it in the wee hours of the night/morning.
Oh yeah, and I'd say the top speed would be like... I dunno, maybe a tad over 40?