Heating Help

Buderus g125be

My old system Burnham v7 with amtrol DHW have some leak installed in 2003, still under warranty. Burnham will replace it with v8. Should I go with the replacement?
I am also think about Buderus G125BE with logamatic 2107 with Buderus SST stainless steel tank 65gallon. Need help on how to configure the system.
Outside reset? main floor reset? Chimney vs direct-vent?
My house is 1994 colonial with 2400sqft. Well insulated with R50 in attic. Double panel window, and all new entry door this years. I will do a heat loss calculation and will compare it with my 3 contractors. I am thinking G125BE 21 should be enough.
Thank in advance for all you help.
sizing
I did my heat loss calculation it come out to be around 55,000 BTU. Here are the three proposals that I got from three different contractors.
1. His heat loss calculation come out 52,000. He want to put in G125be 28 with logamatic 2107, 6 inch stain steel chimney liner, and 40gallon SST stainless steel DHW.
2. His heat loss calculation come out to 75,000 cause he did not factor in the R-19 value of my floor so it is a little off. He want to put in G125be 28 with logamatic, 5 inch stain steel chimney liner, and 40gallon SST stainless steel DHW.
3. He did a heat loss calculation but did not give me a figure. He want to put in G125be 34 with logamatic, 5 inch stain steel chimney liner, and 80gallons DHW.
price wise they are about $1000 different in price. If my heat loss is about 55,000 BTU then why none of my contractor tell me to put in G125be 21. Will this give enough hot water for family of 6. two adult, 2 teen, 2 kids. My wife and my daughter like long hot show. Please help. Thanks.

upgrade?

Will burnham let you upgrade to an MPO boiler for an
extra fee? There are several other manufacturers offering
controls, not just a logomatic. Tekmar is very good, much cheaper
if you need just a basic one too.