Topband: XMT and RCV antenna questions

[David J Rodman MD]

Presently, I have a 160m delta loop (apex up) for my transmit antenna.  
Loop is fed about 30' up one bottom corner and has a 75 ohm coaxial 
matching transformer.  Station has two 140' towers spaced 150' apart but 
orientation is directly N-S.  Some ground radials in ground but very 
extensive enough for exciting the towers without lots of extra work.  
Loop is at 140' tied under the 40m yagi.  Other antennas on that tower, 
including an 80m dipole array.  Phillystran guys.  Antenna oriented SE-NW.

Question:  What antenna is most practical and constructable and 
maintainable at my station considering the physical description?  Right 
now, the loop works has a nice VSWR but is weak on transmit capability.  
(It is possible there is length of feed line with high loss underground 
but in winter this is hard to change.)  The antenna would need to be 
good for DX.

Question:  How much improvement on 160 would be noted  extending a 
beverage antenna  from 475 to 700' or so?  In general, I note other 
stations hear better than I do.  For that matter, is a beverage the gold 
standard of listening antennas or should I be looking at the short loops 
with tuneable directions hung off one of the phillystran guys on the 
towers?  Yes, I know about terminators, feed transformers and the like.

Thanks, Dave.