Yes, that 5 laps thing was a bit of a shock to the system!
I have always had lousy stamina, when I first starting doing some training for VMX I couldn't ride my bicycle for more than 1 km before I had to stop and pant my way back to a state where I could continue. I am usually totally shagged after a 4 lap race. This annoys me no end in Vintage especially. I roll up to the line and look around at all the fat, balding, slow looking guys on the line. At the end of the race, I am shaking, my heart rate is around 250, I can feel fibrillation coming on, sweat is pouring from every part of my body, and I can't move. I've come last.
Meanwhile, the fat, balding, slow old guys all were at the pointy end, they're still fresh, and they're mouthing off about how if there'd just been another couple of laps they'd have got that guy in the lead. It's worse when we ride against young guys, these blokes rip off a 20 minute moto and their hair is still perfectly coiffed, and there is just the slightest trace of manly sweat on their brows...
My regular pedalling, weights, stretching and MTB riding merely serve to make it possible for me to actually finish a 4 lap race. I'll never be able to last a full race at race speed. If races were the first 100 metres only, I'd be competitive.
I think I'll take up dirt track...
As for South Africa, it depends on your track, and number of classes. Lots of classes and a tough track dictate short races, fewer classes and a nice easy open track and you can run longer races. The real issues are firstly can you get through all your classes in a day, then you have to condsider the general fitness and speed of your competitors.