I use stainless steel Soler Points on my speakers. I know Ed Soler and he can make them custom for you. The ones he made for my speakers are 2" wide at the top and about 2.25" tall. I gave him one of the original speaker spikes and he made sure the threads matched on the new spikes. He also makes the pucks to use along with the spikes on hardwood floors if ever needed.
Ed can make them out of brass if you prefer, but the stainless steel ones are the way to go.
What I would suggest is that you measure from the center of the hole where the spikes go out to about 1/8" or 1/4" shy of the edge of the speaker. Mine are 1/4". Then, just decide how tall you want them.
Ed is one of the regulars at the stereo shop here in town and you can place an order through them. My custom spikes are pretty big, though not the biggest he's made for some of the systems I've seen. My spikes were $60 each - again, stainless steel. Ed puts a very sharp point on them, so there is no issue with them penetrating carpet.
Please send me an email if you would like me to help with this, and I can take a picture of my spikes and email them to anyone interested.
And on the question of whether to spike or not, I prefer the tightened bass I get with my speakers spiked.