The single-most important factor of a classroom is the teacher. I don't say this because I am a teacher, but because I've seen the good and the bad. I've seen what teachers can do with little and what they can do with a lot.
The teacher who is a good steward of resources they have will always find the greatest possible successes with students. For example, I often have resorted to making students use their bodies just to show or demonstrate answers. I have them regularly show me with their hands on a scale of 1-10 how well they understand a concept. They know I will reteach if necessary, and caring about their education and enjoying my class, they do make me reteach sometimes.
A well equipped classroom and a nice size is beneficial, no doubt. I currently have one. I can have my students check out laptops for use in the room and I have wireless internet in my room. I have classroom sets of novels, grammar books, literature books and dictionaries but cannot check them out to students. I have a projector and a computer that is loaded with software programs. These are all great features, but I honestly do not use all of them everyday.
Teachers often need training on the technology toys they receive for these types of equipment to be beneficial. Students benefit only when a teacher knows how to use what they have.
Quite often, in times of contract negotiations, teachers cry out for these features: class size and supplies. While relevant, teachers can and should be survivors.
I think that an argument can be made that all classrooms need to be configured differently given the fact that technology literacy is becoming so essential to the modern learner. It is fairly difficult to imagine a student to engage in an authentic learning experience without exposure to technology in any discipline. The idea of being able to learn in a traditional setting when our learners' mentality is different than such a paradigm demands that "well equipped" classrooms include multiple domains and opportunities to effectively use technology. This undoubtedly impacts performance and effectiveness of students and teachers because of the relevant link drawn to students' lives. Instead of creating a classroom that consists of four walls, when technology is effectively integrated, the classroom's dimensions change, in that students can access learning at any time, can collaborate with anyone at any given time. For example, if a student is doing a project on Gary Paulsen, instead of reading news print articles about him, what if they could Skype with him and ask him pointed questions about his work? If a student is trying to seek feedback on a particular point on their work, what if they could blog about it and obtain feedback from all over the world? These learning experiences can only happen with there is a greater emphasis on a "well equipped" classroom through technology use and effectiveness.
I think that part of this depends on the subject being taught in the classroom.
For social studies, for example, the size of the class (I assume that you are talking about the number of people in the class, not the size of the room) and the equipment it has are less important than they would be for science.
For science, it is more important for the teacher to be able to give individual attention to students as they (for example) do their labs. In social studies, that kind of thing is done less often and one on one interaction is less important (but still important).
As far as equipment, science obviously needs more equipment than history or literature classes do.