According to this your amp uses 6L6 or 5881 output (aka power) tubes. Good quality output tubes can last 6 months to two years or more, depends on how often and how hard you push them. You also have a rectifier tube, not sure about the life span on those. NOS preamp tubes can last 10,000 to 20,000 hours or more.
If you play at fairly low volume (say, below 4-5 on the master volume) and get all your overdrive from the preamp section, you may not hear much difference between new production and new-old-stock output tubes. On the other hand, good NOS preamp tubes (your amp uses 12AX7) can make a huge sonic difference. For metal you might be just fine with new production... depends on the tone you prefer, and they all have different tonal and overdrive characteristics. V1 (the first tube in the signal chain) has the most impact on your tone, so you might want to try a few different 12AX7 "flavors" in that position to see what you like.