Tough luck mate, you can't avoid going through Warsaw. Our beautiful capital doesn't even have a ring road.
I don't know the stretch of road from the border to Łomża, never been there. But the remaining part from there on to Warsaw is quite decent for Polish standards (that is, not too many holes in the road).
If you hit Warsaw at around noon, the traffic shouldn't be too heavy. It goes pretty bad again between 3 pm.m and 6.30 p.m. And obviously in the morning, around 9 a.m., it's nightmarish
You will arrive in Warsaw on road no. 8 coming from Wyszkow. The best choice is to keep following the no. 8, it goes around the city centre and is the closest thing to a ring road that we have here.
Keep following the no. 8 (it will probably be marked as going towards Wroclaw) until it links up with the A1 right in the middle of Poland, there you turn onto the A1 (which quickly becomes just "the 1" as it is no longer a motorway down there) and keep following it south. It's quite a nice road, dual carriageway and all.
All along mind the speed cameras, they are conveniently marked with blue road signs saying "Fotoradar". Not all of them are actually active but it's better to slow down when you see that sign until you pass the camera.
Here is a map with descriptions of the roadworks currently in Poland, you can zoom it in. It's got descriptions in Polish, not all of these roadworks are actually a big deal, sometimes it'a just the hard shoulder being done, but in many cases you will need to slow down. I don't know to what extent you understand Polish, perhaps you can understand the descriptions. Do not go for the English version of the website, it's pathetic
http://www.gddkia.gov.pl/article/serwis_dla_kierowcow//index.php
Here is another map that's more user friendly:
http://mapa.targeo.pl/warszawa
if you click on sixth the icon at the top (the "fork and spoon" sign), you'll get a list of different things that can be marked on the map. Tick "Utrudnienia" in the bottom left corner and "OK", that'll put roadworks on the map for you. I don't know to what extent this is up to date, though.
Good luck and don't get depressed travelling through Poland
(Oh, and I'd go for 15" wheels for the miata rather than 16" or 17", it will be much more comfortable on our crap roads. I'm serious, I've swapped 16" for 15" myself!)