IMO those 300W cabs are good only for festival gigs and extreme thumping metal sounds...I love my ~100W 4x12" and use it with a 36W amp.
For years I played a 120W amp into a 140W cab to no ill effects ever. Also used a 50W cab with a 100W Fender tube head for many years...jus was careful to never totally crank it all the way.
Dee
"When life's a biatch, be a horny dog"
Amps: Marshall JVM 410H w/ Plexi Cap mod, Choke Mod & Negative Feedback Removal mod, 4x12", Behringer GMX110, Amplitube 3/StealthPedal
Half a dozen custom built/bastardized guitars all with EMG's, mostly 85's, Ibanez Artwood acoustic & Yamaha SGR bass, Epiphone Prophecy SG, Vox Wah, Pitchblack tuner plus assorted pedals, rack gear etc. for home studio use.