250-500cc some help on my wr 250 2011 please

would anyone recomend using an iridium spark plug for my wr 250? or is there a performance plug youd recomend? if so do you know the code for it? im currently just running the cheap $6 ngk plug.
the reason why im asking is because, my bike can sometimes be a prick to start, on hot and cold starts, i was wondering if a race ready spark plug would help that? ive been using good 2 stroke oil, motul, running 40 to 1, but only running 91 octane fuel do you think if i ran higher octane fuel this may help it starting. the needle and jets are all setup the way they should be.
any thoughts
cheers guys

"the needle and jets are all setup the way they should be." If you elaborate on that it would help.... maybe your pilot jet is too small.

My 300 can be a bear to start sometimes as well. If it takes more than 2 kicks when hot I hold it wide open and it fires within a kick or two......

The biggest change I found to starting was jetting, not the plug. If the pilot was slightly too rich it wouldn't start without holding the throttle wide open and lots of kicking. Now the pilot is perfect it starts 1st or 2nd kick hot or cold. Turning the kick start 1 spline further forward also helps getting more rotation aiding the starting. If you don't like the kickstart in the std position don't try this as it makes more awkward again.

I've found that when the pilot is rich they are harder to start, especially when you stall out in some tight narly technical trail. When the pilot is right its always a quick kick to get it going again - and it seems like it stalls easier when the pilot is too rich.

These guys are correct in recommending jetting changes. Also, you should fine tune the jetting with the air screw. My 10' 300 is super sensitive to elevation, and temperature. At elevation, or higher temperatures, I have to hold the throttle open about half way to start it.