When to go to colder plug (street only driving)

I have TFS 290 heads, stock bottom end (except for ARP main/rod bolts), forged pistons 9.5:1, and a small cam (210 degrees @.050). I have a Cheater N2O plate sitting under a Holley 870 Street Avanger on a Weiand Stealth.
I'm setup to spray around a 150HP (63N20/55F). I have a MSD6AL with a retard box set for -6* on spray. My plugs are NGK FR5 or Autolite 3924. This is a street (and off-raod) only 4x4 truck weighing 5800lbs.

When do I need to worry about going to a colder plug? If I need a colder plug what is recommended (these are 14mm, 5/8 hex, 3/4" reach, gasket type plugs). I run 93 octane pump gas.

I just got this setup and so far don't see any plug issues (but with just a couple of test runs so far).

Thanks

i spray a 150hp hit and my tune is 65n 52f 5.5 fp 28*total timing 110 race gas. im using a stock bottom end cast piston and stock rods and crank. the plug i use is and autolite ar3934 with 150hp hit. i also spray a 50hp hit which is almost as fast about a tenth slower with the 50hp hit i run pump 93 and ar3923 plugs with 42n 36f 5.5 fp 30* total timing. my setup is a dual shot n.o.s system which is 2 stages that can spray the 50hp or 150hp thru the same plate here pic

Nice setup. Do you think a 125 or 150 shot on pump gas is too much?

i have cast piston and try to keep it from detonation so i run 110 when running 150hp hit. i have a friend that runs pump 93 with a 150 hit but also has forged piston and turns the timing down to 24* total you have to turn the timing down and read the plugs he runs a ten heat range plug to 5671a-10 or ar3932

Thanks again for the info.
One of my concerns is how well will my truck run during daily driving with plugs that are several heat ranges colder. Since I only spray occasionally for fun the colder plugs just won't see much action.

run that 50hit tune Monty Smith gave me that tune at drag week works very good on the street used
ar3923 42n 36f 5.5 30* total timing and pump 93. i hope to go in the 10s sept 29 on that tune been close 11.11 run 11.50s on motor. its hard to get a good 60' with the nitrous it blow the tire off so now i have a delay box should get it done on motor 60' are 1,5s on spray 1.8s so ill delay the nitrous alittle hope it works best pass is 10.90s on 150hp hit at 125mph