Uuh ... what patches?   There are many places you might of got patches from but you do not say what or where from.   Are you talking about the example patches created by the late, great Nick Mattocks ages ago as demos of the amp models?

As for no noise gates .... well some folks don't like them as they sound artificial as notes decay and their guitar and cables are quiet enough not to need them.  Some people prefer  a volume control on the floor or guitar volume knob to kill the noise between songs.  I guess whoever created the patches did not feel the need for gates.  I generally use gates for highest gain pathces but I know of  other players who choose to avoid them.

The last bit where you talk about deleting full amp patches .... I am a bit confused.  There are now 30 full amps and 30 pre-amps built into your HD500 (assuming firmware 2.10).  All of the models are available at all times (the 'pre' versions are listed after the 'full' versions) and there is no need to delete one set to use the other.  You can create separate patches using either  full or pre-amp models as you so wish. 

Generally, I would expect the full amp models to sound better but hey, if a Pre-amp sounds good, that is just fine too.   There are no rules, only guidelines.  I would suggest you just import the pre-amp patches into another user setlist and try both.