I've taken a few virgin codeshares from LAX > LHR as a silver over the past couple of months, and in my experiences its hit & miss.

I've always been allowed to check in at upper class. In LAX they usually know and let me through, in LHR they agent always tries to send me to coach, but after telling them, they have always let me through (which is useful because virgin coach lines are long at Heathrow)

As for pre-boarding, sometimes the agents in LAX call for "Virgin gold flying club members and Continental onepass elite members" to board, other times they leave out the Continental part. It’s luck of the draw really, and I've never tried to board early unless they call for continental elites.

Baggage handling, don’t expect "priority handling". But then again, you cant expect this when flying on CO metal either

Overall, the free alcohol in coach, better food, entertainment & service far outweigh any negatives from it being a codeshare (in my opinion).