your choices are the following:
1. material
2. coverage
3. cost
4. weight
material
1. aluminum
2. plastic
3. carbon fiber
i've used the WC full coverage plate on my '05 450X and haven't experience any frame issues. the motor is as stiffer or stiffer than any aliuminum skid plate and it's mounted between those same frame rails.
plastic is light and inexpensive but doesn't provide the same protection as the other materials. it also doesn't reflect as much noise as the other materials.
if noise is a concern you can always use sound proofing material used in autos.
coverage
1. glide plate - minimal coverage
2. full coverage
both will protect the rails of the frame and the lower front and bottom of the engine cases. the full coverage will provide protection to the side cases.
cost
carbon fiber and aluminum full coverage plates are the more expensive options.
weight
plastic, carbon fiber and glide plate types weigh less. aluminum full coverage weigh more.
if plastic type is of interest the Acerbis version is excellent. doesn't use zip ties so it's a more substantial mounting.
http://www.crfsonly.com/catalog/product ... ts_id/3802
works connection makes both a standard glide plate and an extended coverage plate. the standard glide plate doesn't reflect as much engine noise at the extended coverage. the new mounting system helps reduce this as well.:
http://www.crfsonly.com/catalog/product ... ts_id/3481
http://www.crfsonly.com/catalog/product ... ts_id/4351
lightspeed glideplate is light and provides excellent coverage. some report the carbon is brittle but others swear it can take any beating without damage.
http://www.crfsonly.com/catalog/product ... ts_id/3763
bottom line is there are tradeoffs with any choice. you just have to decide which tradeoffs you can live with and which ones you can't. some coverage is better than no coverage. damaged frames and engine cases are expensive to replace.
hope this helps.
ken