FWIW, I travelled from the North of Scotlandland to ride the BCM as my first 600.
I would do the same again, if I went back in time.
Highly recommended.
The issues regarding slow controls are a bit of a non-issue IMHO on a typical 600.
Only the first control will have a bulge of riders; and even then I didn't have any delay at Bronley's. <sp!>
Beyond that, it's spread out, and the controls are not so busy.
It's not PBP, after all.
I've done a few more now, mostly X-rated.
The main difference it makes is organising a sleep-stop yourself.
That might be a hotel, your own house in the case of a DIY, or a ditch / bus shelter according to preference.
Personally, I like a wee bit of comfort and have always arranged for a proper sleep stop, even if it's only for 5 hours sleep.
I don't aim to finish a 600 in a fast time; I aim to use the available time to maximise my sleep-time whilst still finishing with a reasonable margin for mechanicals etc.