Rah rah rah....
If your fitting for a track day/race car, fit only the cage that is the correct application for your car, and that it meets current safety standards, correctly fitted cages are welded in, and never bolted, and should not be modified or drilled in any way..
Tom
You go ahead and spout rubbish and generally get your funk on.
Here's another answer that the OP probably doesn't want to read.
By all means fit an OMP bolt-in cage, but that should be the start of your rollcage, not the finish of it. Provided you are a competent welder then there are various beneficial add-ins you can make to a six-point cage: bar across the car behind the dash, lower door bars, lower cross-brace on the main hoop and harness bars between the cross-bracing. You will also gain quite a lot of stiffness by 'tabbing' the shell and the cage, so it has pick-up points on the windscreen pillars and B-posts.
All this should be done with 'proper' CDS or chro-moly tubing.
The harness bars are particularly important as it's simply not good enough to use rear seatbelt mounts - they're not designed for it, the harness is terminating too far away and if it's the lower mounts, generally too far down. If you are in an impact it'll have a good go at crushing your spine.
Four point harnesses with 2" wide straps ain't good enough either - too thin and no lower securing point, so you'll submarine down in your seat, causing further damage to you. This means that to fit harnesses that will improve your safety you need to fit proper bucket seats with the crutch-strap hole in them.
Oh and you need proper high-density harness padding on the bars to protect the helmet that you're now always going to have to wear when you drive the car.
So, unless you want to bolt in a rollcage and look like some sort of have-a-go-donkey-hero you need to buy in mind that it's just part of a complete safety package - cage, harnesses and bucket seats.
Bit more than a couple of hundred quid on a bolt in cage, isn't it.
